The FOIA was signed into law on July 4, 1966, and has been amended by Congress seven times since then. As the law and its subsequent amendments were introduced, debated, and reported on, a "legislative history" is developed.
You can access below the legislative history of the FOIA, the legislative histories of some of the amendments to the FOIA since its initial passage, and Congressional Source Books which have additional legislative materials and information.
1966 Enactment: Freedom of Information Act
1996 Amendments: Electronic Freedom of Information Act Amendments of 1996
2002 Amendments: Intelligence Authorization Act for Fiscal Year 2003
2007 Amendments: Openness Promotes Effectiveness in our National Government Act of 2007
2009 Amendments: OPEN FOIA Act of 2009 (contained within the Department of Homeland Security Appropriations Act )
Congressional Source Books:
Freedom of Information Act Source Book: Legislative Materials, Cases, Articles (1974)
Freedom of Information Act and Amendments of 1974 (P.L. 93-502) Source Book: Legislative History, Texts, and Other Documents (1975)